1. Field of the Invention
The present invention relates to a resin welded body where a resin part that is transparent with respect to laser light and a resin part that is absorbent with respect to laser light are joined together using laser light and to a manufacturing method thereof.
2. Description of the Related Art
A laser light welding method where a resin part that is transparent with respect to laser light of a predetermined wavelength and a resin part that is absorbent with respect to laser light of the same wavelength are combined and a laser light beam is emitted from the side of the transparent resin part to weld both together is well known.
The principle of this method will be briefly described.
The laser light beam passes through the transparent resin virtually without being absorbed and is absorbed in the vicinity of the surface of the absorbent resin part. The energy of the laser light that has been absorbed is converted to heat and heats the surface of the absorbent resin part. The neighborhood of the surface of the resin of the transparent part contacting the surface of the absorbent resin part is also heated by heat transfer. As a result, a melt layer is formed on the contact surface between the transparent resin part and the absorbent resin part, which results in both resin parts being welded together.
As is apparent from the above-described principle, adhesion between the transparent resin part and the absorbent resin part is important during the welding process. This is because, when the adhesion between both is insufficient, the heat transfer from the absorbent resin part to the transparent resin part becomes insufficient, which leads to defective joining. Usually, in order to ensure surface adhesion between both resin parts, emission of the laser light beam is performed in a state where the transparent resin part and the absorbent resin part are pressure-welded by external pressure at the joint surface (e.g., see JP-A-2004-358697).
As mentioned above, during welding, the force of pressure-welding is applied to the melt layer formed at the joint portion, so melting proceeds at the melted portion until the emission of the laser light is stopped or the application of pressure is stopped. That is, the propinquity of the two parts proceeds. When the distance between the two parts is to be maintained at a predetermined value, a device for precisely detecting the distance between the two parts and a device for instantaneously stopping the emission of the laser light or the application of pressure become necessary. Moreover, the need to individually adjust dimensions with respect to each of the parts arises because there are dimensional variations in the parts. When these are to be realized, extremely expensive equipment becomes necessary.
Further, it is common for the laser light welding method to use a thermosetting resin in order to melt and fuse the resin. With a thermosetting resin, there is no problem whatsoever in the act of melting itself as a common molding method, and a predetermined shape can be created by pouring the resin into a mold using a predetermined pressure. At this time, resin performance such as physical strength and hydrolyzability drop because the resin strength drops if the predetermined pressure is not realized. It is easy for laser light welding to become weak with respect to an ordinary molded product in this point because there is no mold as in molding, the shape of the melted resin is free, and molding pressure is not applied. For that reason, in regard to bodies where extremely high sealedness is required between the two parts, precise control during the joining process and extremely precise dimensional management at the melt surface become necessary, which has resulted in the joining method being expensive.